This invention relates generally to apparatus and methods for connecting optical fibers to integrated optics chips. In particular, this invention relates to apparatus and methods for interfacing optical fibers and integrated optics chips used in forming a Sagnac ring rotation sensor.
Many optical systems include both integrated optics devices and optical fibers. For example one technique for forming a rotation sensor that uses the phase difference between counterpropagating waves in a coil of optical fiber involves forming apparatus for processing and controlling the optical signals on an integrated optics chip and connecting the ends of the coil of optical fiber to waveguides formed in the chip. A Y-shaped coupler is formed at the intersection of three optical waveguides in the integrated optics chip. Light from the light source is input to one of the waveguides, which then guides the input light to the Y-shaped coupler. The Y-shaped coupler then divides the light into two beams that from the counterpropagating waves in the fiber optic sensing coil.
Prior methods of connecting optical fibers to integrated optics chips typically involve forming V-shaped grooves in silicon substrates. To mount a fiber optic rotation sensing coil to an integrated optics chip, the fibers are placed in the V-shaped grooves to position the fibers such that the ends of the fiber optic coil are spaced apart by a distance equal to the distance between the ends of the integrated optics waveguides to which the fibers are to be connected.
To satisfactorily pigtail the optical fibers to the integrated optics chip, both the end facets of the integrated optics chip and the V-shaped grooves must be polished. Angled facets are required for both the V-shaped groove assembly and the integrated optics chip to reduce Fresnel reflections at the butt joints between the optical fiber and the integrated optics chip.
Polarization cross coupling, in which light of one polarization couples into the another polarization is a source of error in fiber optic rotation sensors. In most fiber optic rotation sensor systems the principal axes of the birefringent optical fibers and the integrated optics waveguides must be accurately aligned to minimize polarization cross coupling. Aligning the principal axes is very labor intensive and therefore expensive. In addition, connecting the pigtailed integrated optics chip and optical fiber by conventional methods does not produce a joint that is sufficiently rigid to withstand the severe shocks and vibrations to which a navigation or guidance system including a fiber optic rotation sensor could be subjected.